My son went to daycare from 10 months on as I was a single mom and had to work. This baby will probably have to go to daycare as well, but not for at least a year. I didn't have any problems with that aside from the heartache of not being able to be home with my baby.
I am a teacher, so i am surrounded by germs all the time - and I don't worry about it too much. So healthwise, I can say from personal experience that I got no sicker than I'd been before having a child in daycare.
Emotionally of course it is a very hard decision, and its good you have time to think about it now, though I find the best laid plans go awry with the introducation of a baby to your life.
Financially, daycare is expensive, nannies probably even more so. My son first went to a home daycare. I thought that would be a better atmosphere for him, I later changed him to a daycare center. I found the center to be better. Both were licensed, but it seems the center was better managed as far as routine, santiation, accountability, etc. I also paid for that. I think that the home day care cost me 80.00 a week. When we switched to the center it was 130.00 - big difference. And that was 7 years ago - I know costs have only increased! Still, I doubt you can get a nanny for that much - but maybe. I always wished I had family that could have watched the baby - but no such luck for me.
Good luck!